Understand that a property has only one VALUE; that is determined when a willing Buyer buys it for some amount.
Until that happens, everything else is just OPINION.
My father had a truck he tried to sell; tried for a long time. Kept lowering the price and lowering. Finally, someone offered $800 and my father accepted: Now, it was worth $800, and a bunch of people said that they would have paid a lot more. My father thought it was worth a lot more too! But it was worth $800, and no a penny more.
Realtors do CMA's and Appraisers do APPRAISALS to determine the WORTH of a property so that we can price it with some intelligece; we can document it's WORTH for Buyers and Lenders: But even this is just OPINION.
Some Web Sites have their own method for attaching a VALUE to a property; sometimes with good results, sometimes not. The data has be current, approximate, and relevant.
Good luck and may God bless